To better understand what osteoarthritis is, let's first take a look at what a joint is and how it works.
Your musculoskeletal system contains muscles, bones and associated tissues that move your body and maintain its form. Wherever two or more bones come together, a joint is formed. For example, your knee joint contains three bones - the femur or thighbone, the tibia or shinbone, and the patella or kneecap. Your hip is a ball-and-socket joint between the head of the thighbone and the pelvis. And your wrist is actually a linkage of 10 separate bones.
Bones are held together with strong bands called ligaments. Muscles cross the joints to provide active support and movement. Tendons attach muscles to bones. When a muscle contracts, it moves the bones like levers at the joint. Strong muscles protect the joints they cross by acting as stabilizers and shock absorbers.
Your joints are also lined with a sensitive membrane called the synovium (sin-OH-vee-um). This membrane's job is to produce a few drops of fluid, called synovium fluid, that lubricates the joint. A normal healthy knee joint, for example, usually contains about one half teaspoon of synovial fluid.
Cartilage is the tissue that covers the ends of the bones and forms the joint's surface. It is a remarkable tissue. Hyaline cartilage is the strong, slippery contact where motion occurs at your joints. And it is this cartilage that can become affected by osteoarthritis.
There are no blood vessels in cartilage. Here the synovial fluid and underlying bone nourish the cells. There is also no nerve endings in cartilage. So the actual fraying and cracking of worn cartilage is not really the source of pain. Instead, osteoarthritis symptoms arise from inflammation or strain in the structures that surround the joint.
In my next post, I'll discuss what osteoarthritis is and why it hurts.
[The above article was taken from excerpts from Know Your Bones: Making Sense of Arthritis Medicine, a guidebook written for those who suffer from osteoarthritis.]